Equipment currently available to the adhesive industry for use in processing hot melt adhesives is designed and manufactured to operate at high pressures and at high temperatures, e.g., up to 450° F. These units are designed to heat to a molten state hot melt adhesives that are then transported for application to a substrate surface. Such adhesives are conventionally applied at high temperatures, i.e., temperatures greater than 300° F., up to about 350° F. or higher.
Conventional hot melt adhesives require temperatures greater than 300° F. in order to ensure complete melting of all the components and also to achieve a satisfactory application viscosity. Even when processing conventional hot melt adhesives using conventional equipment, problems such as adhesive stagnation and air pocketing occur. This contributes to char formation and related overheating problems which adversely affect dispensing performance. Frequent down time, trouble shooting and maintenance, as well as part replacement is required and is costly. The need for high temperature also increases operator's risk with respect to both burns and inhalation of residual volatiles. In addition, high temperatures require more energy, placing greater demands on the manufacturing facility.
Recent innovations in adhesive chemistry have resulted in adhesives that can be applied at lower temperatures, i.e., temperatures less than 300° F. Processing and dispensing of low application temperature adhesives require certain considerations not encountered when processing conventional hot melt adhesives.
First, lowering the application temperature is known to increase the viscosity of conventional hot melt adhesives resulting in greater wear and tear to processing equipment. This adhesive is formulated to achieve the balance of low viscosity and performance required to maintain package integrity. Second, low application temperature hot melt adhesives are formulated with tackifiers which are typically unstable and known to accelerate wear to processing equipment. Third, due to their low processing and melt point temperature requirements, the adhesive would be expected to block if conveyed through an auto feed unit. Fourth, the dispensing tube on the autofeed unit would be expected to be longer in length than those used to process conventional hot melt adhesives in conventional processing equipment due to both conductive and convective heating and condensation on high temperature volatiles.
There exists a need in the art for an integrated system that can be used to process low application temperature hot melt adhesives for, e.g., packaging operations such as for forming and/or sealing and closing operations for cartons, cases or trays. The current invention fulfills this need.